This invention relates generally to the microbiological leaching of ore in a heap and is concerned, more particularly, with the simulation of certain aspects thereof.
In a microbiological heap leaching application mined ore is crushed and agglomerated with acid and nutrients. Oxygen and carbon dioxide are supplied to the ore to provide an environment for organism growth and to promote the oxidising conditions required for mineral degradation.
Normally the acidic solution is applied to the top of the ore heap and is allowed to percolate downwardly while the oxygen and carbon dioxide are supplied in the form of air introduced to the bottom of the heap. The air flowing upwardly and the acidic solution flowing downwardly, through the heap, are counter-current transport media which interact at different points of the heap allowing oxygen transfer, species migration and a heat exchange mechanism within the heap.
It is known that a heap leaching process is temperature-dependent with determining factors including the ore type and the microorganisms which are used for the leaching. For example, the acidic solubilisation of copper from copper oxide ores, chalcocitic ores and other secondary copper sulphide bearing ores, at low temperatures, may result in an acceptable recovery of the metal. On the other hand minerals such as enargite, carrollite and chalcopyrite are slow leaching at low temperatures (below 30° C.) and leaching at these temperature results in poor metal extraction which, in most instances, is uneconomical.
The enhanced oxidation of the sulphide components of minerals of the aforementioned type, by microbiological action, is an exothermic reaction which releases substantial amounts of energy, a process which must be correctly managed to obtain effective metal recovery.
It is difficult and expensive to monitor conditions inside a commercially operated heap due, primarily, to the size of a typical heap and the amount and type of material it contains.